Miniaturization of electronic components has been an on-going trend in the electronics industry. The consuming public demands more processing and capabilities in smaller and smaller packages. While many electronic functions can be transistorized, certain electronic functions, such as frequency control devices, present packaging challenges. This challenge is further complicated when certain components require isolation from other components in the same package.
For example, crystal resonators are used for providing highly precise frequency references for many applications. Piezoelectric quartz crystal resonators are commonly implemented in such oscillators to provide highly accurate timing signals for communications, navigation and radar applications. The piezoelectric devices, such as piezoelectric quartz filters, piezoelectric quartz resonators and the like, typically include a piece of piezoelectric material mounted to a substrate. The quartz element can have thin metallic electrodes attached to it through which electrical signals are coupled into and out of the piezoelectric quartz material. Common problems with piezoelectric devices are adequately isolating the piezoelectric device from mechanical shock and dealing with thermal expansion coefficient mismatches between the piezoelectric material and the substrate material.
There have been attempts to alleviate some of the problems described herein that have had only limited success. A dual cavity package has been implemented in the AT&T TRU-200 package. In addition, the ‘H-package’ is described in U.S. Pat. Nos. 5,500,628 and 5,405,476. The H-package uses thick film technology and has a hermetic bottom cavity on one side that is disposed to have the additional non-hermetic cavity. There are several references that illustrate some form of package shelves, namely the chip carrier of U.S. Pat. No. 4,903,120 and the high density package of U.S. Pat. No. 4,943,844. Stackable packages are described in U.S. Pat. No 6,518,659. Multiple chamber or cavity packages of some form are depicted in U.S. Pat. Nos. 4,985,687; 4,627,533; and 5,729,181. Other references include U.S. Pat. Nos. 5,771,556 and 6,133,674.
The state of the art suffers from the problem of how to incorporate the individual components of a larger package into a smaller package. One possible solution is a package design that suspends a substrate to a package by mounting on shelves. Such a design can employ the thick film as well as thin film or flex circuit technology and allow high performance components such as inductors, capacitors, and varactors to be incorporated.